Numbers 3:8
And they shall keep all the instruments of the tabernacle of the congregation, and the charge of the children of Israel, to do the service of the tabernacle. And they shall keep all the instruments of the tabernacle of the congregation, and the charge of the children of Israel, to do the service of the tabernacle.
The verse assigns the Levites to keep all the instruments and furnishings of the tabernacle and to do its service on behalf of the children of Israel. This charge was appointed by God rather than left for any tribe or person to choose, and it taught Israel to regard the tabernacle and everything belonging to it as holy. God gave the Levites this honored service because they took no part in making and worshiping the golden calf and faithfully carried out His order of judgment upon the idolaters.
Their work included erecting the tabernacle and encamping immediately around it while the hosts of Israel pitched at a distance, and when Israel journeyed taking it down and bearing it with the ark and the candlestick and the other sacred articles of furniture. This Levitical service was distinct from the priesthood, which was given to Aaron and his sons, so Korah's standing as a Levite did not give him the priestly office. The honor of the appointment stirred ambition for still higher office and greater influence with the congregation, leading Korah and sympathetic Levites to seek the priesthood for themselves.
Much later, Elkanah as a Levite remained especially devoted to this assigned service, but the irregular and incomplete worship at Shiloh left him with no regular employment at the tabernacle.